A computerized system which utilizes the Serial ATA interface for disk drive storage typically includes a host, a set of Serial ATA disk drive assemblies and a set of Serial ATA cables connecting the host to the set of Serial ATA disk drive assemblies. In the context of a data storage system, the host typically takes the form of a motherboard containing, among other things, (i) processing circuitry configured to perform data storage operations (e.g., caching operations, read and write operations with the set of Serial ATA disk drive assemblies, etc.) and (ii) Serial ATA motherboard connectors which provide Serial ATA access to and from the motherboard, i.e., electronic access in accordance with the Serial ATA interface specification. Additionally, each disk drive assembly typically includes (i) a disk drive chassis (or housing), (ii) a disk drive unit mounted to the disk drive chassis, and (iii) a Serial ATA disk drive connector which is also mounted to the disk drive chassis and which provides Serial ATA access to and from the disk drive unit. The set of Serial ATA cables includes wires which are terminated at each end with Serial ATA cable connectors to interconnect the host with the Serial ATA disk drive assemblies. At least a portion of the Serial ATA interface specification is described in a document entitled “Serial ATA: High Speed Serialized AT Attachment”, Revision 1.0a, Jan. 7, 2003, the teachings of which are hereby incorporated by reference herein in their entirety.
To construct the data storage system, an installer typically fastens the set of Serial ATA cables to a main support (e.g., a standard electronic equipment rack, a custom-sized cabinet or frame, etc.). The installer then fastens the motherboard to the main support and connects the Serial ATA motherboard connectors of the motherboard to corresponding Serial ATA cable connectors at one end of the set of Serial ATA cables. The installer then attaches the Serial ATA disk drive assemblies to the main support and connects the Serial ATA disk drive connectors of the disk drive assemblies to corresponding Serial ATA cable connectors at the other end of the set of Serial ATA cables. Typically, the chassis of the disk drive assemblies are designed so that the disk drive assemblies easily slide into and out of the main support to facilitate servicing (e.g., for hot swapping, replacement, future upgrading, etc.).
In contrast to the above-described relatively simple Serial ATA disk drive assemblies, some equipment manufacturers provide enhanced Serial ATA disk drive assemblies which, in addition to listed components of the above-described simpler disk drive assemblies, further include (i) a second Serial ATA disk drive connector and (ii) a daughter card which interconnects between the two Serial ATA disk drive connectors and the disk drive unit. The daughter card includes a multiplexer that is capable of switching between the two Serial ATA disk drive connectors thus enabling two hosts to have access to the disk drive unit, i.e., a first host through one Serial ATA disk drive connector and a second host through the other Serial ATA disk drive connector. Such enhanced disk drive assemblies enable data storage systems to utilize a primary host and a backup host for fault tolerance purposes. In particular, if the primary host fails (e.g., crashes), the backup host then begins operation. In such a situation, the device-side multiplexers of the disk drive assemblies switch selection from the Serial ATA disk drive connector leading to the primary host to the Serial ATA disk drive connector leading to the backup host to provide the backup host with access to the disk drive units of the disk drive assemblies thus enabling the data storage system as a whole to remain in operation.